The present invention relates to a magnetoresistive head (hereinafter referred to as an MR head), which comprises a ferromagnetic magnetoresistive effect element (hereinafter referred to as an MR element) making use of a ferromagnetic magnetoresistive effect for reproducing magnetic information written in a magnetic recording medium.
As is well known in the art, the MR element is capable of producing a high level output independent of the relative velocity of the element and recording medium, and its application to a reproducing head of small size and high density magnetic recording apparatus has been in focus. For the practical use of the MR element to the head for reproducing magnetically recorded signals, it is necessary to meet two basic requirements.
A first requirement is that the MR element is capable of linear response to the magnetic information written in the magnetic recording medium. To this end, in the MR head a bias magnetic field is applied in a direction orthogonal to a sense current flowing in the MR element (hereinafter referred to as transversal bias magnetic field) so as to set the angle .theta. between the sense current and the magnetization M of the MR element (hereinafter referred to as bias angle) to a predetermined value (desirably 45 degrees). For providing the bias magnetic field, various methods have been proposed. U.S. Pat. No. 3,864,751 discloses a structure, in which a soft magnetic bias-assistant layer or a soft adjacent layer and an MR element are laminated with an intervening electric insulating layer. This United States Patent also discloses a method, in which a soft bias-assistant layer is magnetized by supplying a sense current to the MR element, while using a magnetic field generated by the soft magnetic bias-assistant layer to apply the transversal bias magnetic field to the MR element. As another bias means, Japanese Utility Model Laid-Open No. 159,518/1985 discloses a structure, in which a non-crystalline soft magnetic bias-assistant layer and an MR element are laminated with an intervening non-magnetic conductive layer. In this structure, the resistivity of the non-crystalline soft magnetic bias-assistant layer is extremely high compared to the resistivity of the MR element. Thus, a major portion of the sense current flows through the MR element, so that it is possible to obtain substantially the same bias effect as obtainable with a structure, in which the non-crystalline soft magnetic bias-assistant layer and MR element are electrically insulated from each other. According to this bias method there is no need of maintaining the electric insulation between the non-crystalline soft magnetic bias-assistant layer and MR element, thus permitting the formation of a compact MR head with a reduced thickness of the non-magnetic conductive layer.
The second requirement is to suppress Barkhausen noise, which is a main cause of reproduced signal noise and deteriorates the quality of the reproduced signal. The Barkhausen noise is thought to stem from the movement of magnetic walls generated by an inverse magnetic field at an end of the MR element. Accordingly, there have been proposed a number of methods of eliminating the magnetic walls by making the MR element part to be of a single domain. Japanese Patent Laid-Open No. 40,610/1987 discloses a structure, in which an anti-ferromagnetic material is provided at each MR element end to make use of mutual exchange action of the two portions of the anti-ferromagnetic material for applying a bias magnetic field in the sense current direction (hereinafter referred to as longitudinal bias magnetic field).
For generating the bias magnetic field with the anti-ferromagnetic material, there are several restrictions. A first restriction is that it is necessary to form the anti-ferromagnetic layer in direct contact with the ferromagnetic magnetoresistive effect layer since the bias magnetic field is generated with the exchange force. A second restriction is that the anti-ferromagnetic material has to be patterned such as to be present only at opposite end portions of the MR element. This is so because if the exchange force is active over the entire MR element, the response character thereof is deteriorated due to a high anisotropic magnetic field in the inverse magnetic layer. To meet the above two restrictions, as shown in FIG. 3, the ferromagnetic magnetoresistive effect layer 4 and anti-ferromagnetic layer 3 are formed continuously in vacuum, and then only the anti-ferromagnetic layer 3 is etched. In this patterning, however, it is difficult to selectively etch only the anti-ferromagnetic layer 3. In addition, an over-etching will result in deterioration of the characteristic of the ferromagnetic layer. In FIG. 3, 1 is a non-magnetic substrate, 5 is a non-magnetic conductive layer, 7 are electrodes, and 6 is bias-assistant layer.